In recent years, wireless communications advance rapidly, and all sorts of new technologies have been developed, from 3G in cellular communications, to Local Multipoint Distribution Services (LMDS) and Multichannel Microwave Distribution System (MMDS) in Broadband Wireless Access, further to WLAN Authentication and Privacy Infrastructure (WAPI), IEEE 802.11b, 802.11a and 802.11g in Wireless LAN. With wireless communication technologies, the world has become smaller than ever before. New concepts and new products, including ubiquitous network terminals, people-oriented customized and smart mobile computing, and convenient and rapid wireless access and wireless interconnection, are fitting into people's work and life. Various consumer electronics, such as mobile phones, Personal Digital Assistants (PDAs), laptops and digital cameras, have become a part of people's life. As the peripheral devices increase, it turns into an annoying problem to realize information sharing between these devices in a limited and changeful office or home environment with low cost and simple measures. Wireless Personal Area Network (WPAN) is a new wireless communication technology to solve this problem that requires limited operation area, supports a variety of service types and serves a particular group, and to realize seamless wireless connections.
As a wireless network with a smaller coverage than Wide Area Network and Local Area Network, WPAN has become an important component in communication networks. WPAN is also a prominent technology in 4G wireless communications and control, and supports seamless connections with various air interfaces in 2G and 3G mobile communications. If we say that the access network is the “last kilometer” to digitalization, then WPAN must be the “last 50 meters”. WPAN provides in the Personal Operating Space (POS) seamless wireless connections with a variety of service types and serving a particular group. The POS is a small region in proximity to an individual, typically having a radius of 10 meters, where communication is accomplished based on Ad hoc. The POS is tied to a person, particularly to a handheld operated by the person, and moves along with the person. WPAN provides for devices in the POS the ability to communicate, and allows them to communicate with other devices entering the POS. WPAN can form naturally when needed, without user intervention, and provides interoperability with established networks or independent networks. WPAN also supports authentication and secure operation modes, permitting rapid connections with authorized personal devices and preventing connections to other unauthorized devices. WPAN is intended for the personal use market, realizing convenient and rapid data transmission among consumer electronics, and thus having the advantages such as cheap, small in size, easy to use, and energy-efficient.
To access a WPAN, a device has to connect with a coordinator in the WPAN. The coordinator provides for the device access to the WPAN and routing functions. Normally, the coordinator itself may also function as a terminal. There are three access methods for WPAN:
Access method 1: the device accesses the WPAN in a non-secure mode and obtains a network address, then communicates with other devices in the WPAN; or, the device obtains a secure service key from the WPAN then performs secure communication with other devices in the WPAN.
Access method 2: the device performs a security operation on the association process using a pre-shared key, and if the coordinator can desecure the security operation, the coordinator allows the device to access the WPAN, and the device accesses the WPAN in a secure mode and obtains a network address.
Access method 3: the device accesses the WPAN in a non-secure mode and obtains a network address, then performs authentication with a WPAN administrator, and if the authentication succeeds, the device is allowed to access the WPAN; otherwise, the device is removed from the WPAN.
The access method 1, which is enough for WPANs requiring no security or WPANs where only secure communication is needed, is an optional access form in establishing a WPAN. The access method 2 requires pre-sharing of a session key, and due to its lack of randomness, the pre-shared session key is easy to be cracked, therefore the access method 2 is of poor safety. The access method 3 requires authentication between each device to access the WPAN and the WPAN administrator, resulting in high communication traffic and low efficiency; in addition, any device may launch a DoS attack, that is, to access the WPAN in a non-secure mode and obtain a network address then performs authentication with the WPAN administrator, which is ended with authentication failure.
In the layered model of network, the layers follow a strict one-way dependency, and division and cooperation of the layers reflect on the interfaces between neighboring layers.
“Service” is an abstract concept describing the relationship between neighboring layers, that is, a group of operations provided by a layer to the layer above it. The layer below is the service provider, and the layer above is the user requesting services. A representation of service is primitive, such as a system call or a library function. A system call is a service primitive provided by a system core to a network application or a high-layer protocol. An (N)-layer always provides to an (N+1) layer a service more complete than an (N−1) layer; otherwise the (N)-layer is needless.